The word caries is derived from latin, meaning rot' or decay . It is similar to the Greek word ker meaning death. Dental caries is defined as an infectious microbiologic disease of the teeth that results in localized dissolution and destruction of calcified tissue. There is presently alarming rate of increase in the prevalence of dental caries in developing countries. Dental caries is a multi factorial disease in which there is an interaction between three principal factors, a. A susceptible Host tissue (b) Micro flora with a cariogenic potential (c) A suitable local substrate. In addition a, fourth factor time, must be consider. All the factor must be present and must interact with each other for dental caries develop. A variety of microbial factors have been associated with dental caries activity. Varies observation indicate that a causal relationship between Streptococcus Mutants and the development of the early carious lesion of enamel. Lactobacilli, however seem to be associated with dentinal caries and Actinomyces strain with root surface caries. The word epidemiology derived from the Greek word, Epidemic. Epi means upon, demos means people and logos means study or science."